1. Field of the Invention
The present invention relates to a cylinder liner for a multiple-cylinder engine.
2. Description of the Related Art
In recent years, it has been known to provide a cooling structure for a cylinder liner flowing cooling liquid in grooves arranged at either one or both of an outer circumferential surface of the cylinder liner and an inner circumferential surface of a cylinder bore in a cylinder block. This is due to the fact that a cooling control can easily be carried out according to positions in the cylinder liner as compared with the jacket type cooling structure applied in the past.
For realizing a proper cooling according to parts in an axial direction of the cylinder liner, for example, Japanese Utility Model Publication No. 3-29560 (Application No. 62-60967) has proposed a cylinder liner formed in its outer circumferential surface with a plurality of groups of annular grooves. The cylinder liner has a plurality of groups of annular grooves at its outer circumferential surface and has longitudinal grooves communicating the annular grooves and forming an outlet and an inlet for a cooling liquid at the surface, wherein the outlet communicates in series with the inlet in adjoining groups of annular grooves and total sectional areas of the annular grooves in the groups of annular grooves are decreased from a lower part toward an upper part.
With the foregoing, a flow of cooling liquid directed from the upper part of the cylinder liner to the lower part thereof will be described, wherein the cooling liquid flows around the outer circumference of the cylinder liner through the annular grooves in a group of annular grooves, thereafter moves from the longitudinal groove forming the outlet of the group of annular grooves toward the longitudinal groove forming the inlet of the adjoining next stage group of annular grooves, flows from the longitudinal groove into the annular grooves of the group of annular grooves, flows around the outer circumference of the cylinder liner, then the cooling liquid is moved to the lower adjoining group of annular grooves in the same manner.
In this case, since the total sectional areas of the annular grooves in the groups of annular grooves are decreased from the lower part toward the upper part in the cylinder liner, a flow speed at the group of annular grooves at the upper part of the cylinder liner is increased, a coefficient of heat-transfer of the cooling liquid at the upper part of the cylinder liner is increased, and a cooling capability at the upper part of the cylinder liner is increased, which performs an appropriate cooling corresponding to a temperature gradient in the axial direction of the cylinder liner (high at the upper part and low at the lower part).
However, even in the case where the cylinder liner with grooves of this kind is used in the multiple-cylinder engine, it has a tendency that parts in directions of major-thrust and minor-thrust tend to be cooled while parts in an axial direction of a crankshaft cannot be sufficiently cooled. Because of this, a temperature distribution in a circumferential direction of the cylinder liner becomes uneven. A temperature difference in the circumferential direction is large in the upper portion of the cylinder liner.
For solving the aforesaid problem, a cylinder liner in which an outer circumferential surface of the cylinder liner has a cylindrical shape, and the bottom of a circumferential groove has an elliptical shape having a long axis which is parallel to an axial direction of a crankshaft and a short axis which is parallel to directions of major-thrust and minor-thrust has been previously proposed in Japanese Patent Laid-open No. 3-78517 publication. This cylinder liner is characterized in that the flow speed of a cooling liquid flowing in the circumferential groove becomes large at the part in the axial direction of the crankshaft and a cooling capacity of said part is large.
However, the cylinder liner of this kind is not uniform in the wall thickness in the circumferential direction to pose two problems that a circularity of the inner circumferential surface of the cylinder liner is hard to obtain, and that cam machining is required to machine a circumferential groove and the production is not easy.